The present invention relates generally to the charging of particulate matter into a gas stream.
More particularly, the invention relates to a method of charging particulate matter, such as small coal particles, into a gas stream, such as a gas stream flowing in a flight stream tube.
The invention also relates to apparatus for carrying out the method.
In modern coke-making it is becoming increasingly common to use preheated coal particles for the coke oven charge. There are various reasons for this, one of these being that this technique permits the use of poor coking coal, i.e. of coal which inherently does not have good coking characteristics.
The coal to be preheated is comminuted to small particle size and is then admitted in moist condition into a preheating installation, for example an upright flight stream tube, in which it is dried and preheated to temperatures of about 100.degree.-500.degree., preferably about 300.degree. C. The preheating and drying can be carried out in a single stage, in dual stages or in multiple stages; it is accomplished by contacting the coal particles with hot heat-carrier gases which release their sensible heat to the coal particles and are then wholly or in part discharged to atmosphere.
A significant problem encountered in this coal treatment resides in the lack of uniformity of coal-particle distribution throughout the heat-carrier gas stream. To obtain uniform and acceptable results, a uniform charging of coal particles into--and distribution thereof in--the gas stream is of great importance in each and every drying and preheating stage, respectively. When flight stream tubes are used, the uniformity of coal distribution in the gas stream flowing in the tube is the more important, the shorter the tube is. Real reliability of uniform coal distribution in the gas stream has not heretofore been attained; rather, due to a "separation" phenomenon a condition occurs in which there are concentrations of coal in some parts of the gas stream cross-section and little, if any, coal in other parts thereof. The result is differential heating of different parts of the tube wall, leading to twisting and buckling of the tube and ultimately resulting in substantial damage to the same.
A proposal to mitigate this problem has been made in German Allowed Application DE-AS No. 2,427,932 according to which the flight stream tube is provided with a constriction formed by a tube section of rectangular cross-section, one of the two longer sidewalls of which is provided over its entire width with a charging inlet for the coal particles. Downstream of the constriction the tube is provided with a diffusor, the cross-section of which changes in downstream direction from rectangular to circular shape. This construction provides certain advantages, but it still does not prevent the aforementioned separation with its disadvantageous consequences.